Wikipedia said:In each case, crab spiders use their powerful front legs to grab and hold onto prey while paralyzing it with a venomous bite.
2 claws with Imp Grab sounds good. Want to add an automatic bite when grappling?
Lots of Dex damage, perhaps. So it can Dex to 0 in one or two bites, then coup de grace.
Since these guys are huge and monstrous, I'd be happy with giving them actual claw attacks, much like the tentacles of giant squid actually dealing damage as opposed to their smaller brethren.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.